The present invention relates to a device for switching or diverting the flow of cleaning fluid in a drill string. In particular, the switching device allows cleaning fluid being pumped through a drill string to the lower sections of a well bore to be selectively diverted to the upper sections thereof.
Oil, gas, water and other types of wells are usually lined with a steel pipe or well to ensure the integrity of the well bore hole. From time to time during the working life of the well it is necessary to clean the internal walls of the well casing to remove debris and residues, such as oil, and scale, which have accumulated thereon. Various cleaning tools are known within the prior art for effecting a mechanical cleaning action on the internal walls of a well casing. Typically, these comprise brushes and/or scrapers mounted on a usually cylindrical carrier which can be connected to a drill string to drive the cleaning tool through sections of the well casing.
It is also known within the prior art to enhance the cleaning action of mechanical cleaning tools by introducing chemical agents into the well bore, either before or during the mechanical cleaning operation. These chemical agents attack and loosen the debris and residues attached to the well casing and thereby generally enhance the cleaning efficiency of mechanical cleaning tools.
In order to remove debris and residues loosened from the internal walls of the well casing it is known in the prior art to circulate cleaning fluid from the surface of the well down through the drill string carrying the mechanical cleaning tool, out into the annular space between the well casing and the drill string, and then back to the surface. This circulating cleaning fluid flushes the debris and residues loosened from the well casing back up to the surface where they can be filtered out and removed.
In order maximise the cleaning efficiency of chemical cleaning agents it is necessary for the cleaning fluid circulating through the well bore to be in turbulent flow. The degree of turbulent flow within a well bore is a function of the diameter thereof. It is not unusual for the internal diameter of a well bore to be larger at the top or mouth than it is in the lower reaches thereof. It follows that the flow rate required to achieve turbulent flow will be reached in the lower, narrower sections of the well bore well before it is reached in the upper, wider sections thereof. This can create problems, particularly where the fluid pumping equipment at the surface is operating at or close to its maximum pumping pressure in order to circulate fluid through the well bore fast enough to achieve turbulent flow in the lower reaches thereof. Put simply turbulent flow will not be achieved in the upper, wider section of the well bore.
It is an object of the present invention to provide a fluid flow switching device which enables an operator to selectively divert the flow of clearing fluid being pumped through a drill string to an outlet in the switching device.
According to the present invention there is provided a fluid flow switching device for use in a drill string comprising a tubular member or pipe adopted in use to be connected at each end to a respective section of a drill string so as to be continuous therewith, a sleeve member axially slidable within the tubular between a first upper position in which a port in the side thereof is in alignment with a port in the side of the tubular member and a second lower position in which the port in the side of the tubular member is obstructed and closed by the sleeve member, a plurality of fingers each of which is pivotably connected at one end to the lower end of the said sleeve and which at the other end defines one segment of a segmented circularly closure member, the segmented closure member being closed when the fingers are pivoted radially inwardly to bring the segments together and being open when the fingers are pivoted radially outwardly to separate the segments, and an annular operating surface positioned within the tubular member beneath the sleeve member, which annular operating surface diverges radially outwardly from the upper end thereof towards the lower end thereof and over which the said plurality of fingers are axially slidable as the sleeve member is moved between the said first upper position, wherein each of the plurality of fingers is biased radially inwardly causing the segmented closure member to obstruct the tubular member, and the said second lower position, wherein each of the plurality of fingers is biased radially outwardly causing the segmented closure member to open.
Preferably, each of the said plurality of fingers is biased radially outwardly thereby ensure that the said segmented closure member is normally in an open position.
Preferably, the fluid flow switching device further comprises a swivel piston mounted in the tubular member for engagement with the said sleeve member to move the said sleeve member between the upper and lower positions. Conveniently, the swivel piston comprises a bayonet fitting having at least one pin and the sleeve member defines at least one slot with which the said at least one pin engages and travels through to move the sleeve member from the second lower position to the first upper position and then back to the second lower position
In use the fluid flow switching device is connected into a drill string at a point along its length which ensures that when the drill string is located in a well bore the device itself lies in the region of the upper, larger diameter section of the well bore. Now, to achieve turbulent flow in the upper, wider diameter section of the well bore, the fluid flow switching device is operated to close the flow of cleaning fluid into the section of the drill string connected below the device, and thence to the lower, narrower sections of the well bore, and to open the port in side of the device such that cleaning fluid is vented directly into the upper, larger diameter section of the well bore. Since the cleaning fluid is vented directly into this larger section the pump pressure required to achieve turbulent flow is reduced (when compared with that required when the cleaning fluid has first to be pumped past the narrow section). Thus, it is possible to achieve turbulent flow within the larger section without exceeding maximum pumping pressure limits.